Discussion
ERWT in the spine is very rare. ERWT occurring within teratomas (5-10) is pathologically described as teratoid Wilms tumors and separate entities from the classic ERWT described in this case report. No elements of teratoma were found in our patient.
Posalaky et al. (11) described nephrogenic rests in the spine and suggested that these cells could undergo malignant transformation. There was no associated spinal dysraphism in their two reported cases, and the nephrogenic rests identified in the spine were benign with no evidence of ERWT. However, ten years later, Fahner et al. (12) described ERWT in the spine without spinal dysraphism.
The association of spinal dysraphism with ERWT is explained by the embryonic rest hypothesis of cancer development (13). This theory states that remnants of embryonic tissue occur in adults and children and that a change in the surrounding tissue would allow the embryonic tissue to resume proliferation and to produce masses of cells that resemble fetal tissues (14). Thus, it has been proposed that ERWT arises from pluripotent (mesenchymal) cell rests that undergo malignant transformation (13,14). Fernbach et al. (15), citing Grobstein’s (16) study, suggested that the embryonic central nervous system is capable of inducing nephrogenic differentiation in the embryonic mesenchyme from which the spine develops. Furthermore, Deshpande et al. (17) reported an ERWT within the dorsal lumbar spine’s subcutaneous fat without associated spinal dysraphism, very similar in location to the nephrogenic rests described by Horenstein et al. (18), both of which had no associated spinal dysraphism.
The abortive formation of nephrogenic elements and the location of the tumor in the bifid spine outside the path of the developing kidneys, as in our case, supports the hypothesis that mesenchymal rests trapped in the wrong location and under aberrant stimulation develop into nephrogenic rests that undergo malignant transformation into ERWT. (13)
In a review of 34 cases of ERWT, Coppes et al. (19) analyzed therapy and survival. They suggested that all patients with ERWT receive postoperative chemotherapy, with the same regimen as for a renal Wilms tumor of the comparable stage. Sastri et al. (20) reviewed three additional cases and summarized a total of 48 cases of ERWT, and concurred with the recommendations of Coppes et al. (19). Based on these recommendations, our patient was treated according to the latest guidelines for renal Wilms tumor, following the National Wilms Tumor Study-V regimen for EE4A.